Modern aircrafts generally include an onboard computing system called flight management system (FMS). The FMS provides the flight crew with information on the future states of the aircraft along a selected flight path. This information includes predictions based on the performance of the aircraft during various phases of the flight. Typically, the flight plan includes a descent phase, which normally starts from the end of cruise (also referred to as top-of-descent distance) and is considered to be completed once the aircraft reaches a runway threshold through an approach phase, which is mainly performed at idle thrust. Predictions of time, fuel consumption, flying altitude, aircraft speed and other parameters at en route points until the runway threshold provide useful information about the future performance of the aircraft. Typically, such predictions are displayed to the flight crew and used in the guidance of the aircraft along the vertical trajectory.
Currently, the criteria used for obtaining the information are preset or the parameter values may be assumed in obtaining the information. For example, climb angle, fuel flow and true air speed (TAS) may be considered to vary linearly with the altitude. Further, constant values may be considered for parameters, such as air speed, lapse rate, temperature and the like to obtain the information. This can result in providing inaccurate information to the flight crew during the descent phase.